updated actions

changing peaceiris/actions-gh-pages from @V3 to @v4

Author: kierisi

.github/workflows/build-docs.yml

@@ -40,7 +40,7 @@ jobs:
 
       - name: Push to gh-pages branch for publication from main
         if: github.ref == 'refs/heads/main'
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./_build/html